Electromagnetically clutched press

ABSTRACT

A spindle press drive assembly using an electric motor&#39;&#39;s rotor as an energy storing flywheel is characterized in that the electric power drives a second rotor acting as an energy storing flywheel and which is electromagnetically coupled to the first rotor so as to provide rotational energy therefor from the kinetic energy stored in the second rotor. The two rotors are disconnected at the end of the working stroke so that the second rotor remains rotating and only the energy of the first rotor is used during pressing. The two rotors may be coaxial or concentric and the second rotor may be independently rotated or rotated by electromagnetic forces between the two rotors. The disconnection can be achieved by a switch which senses the axial force occuring during deformation of a workpiece.

United States Patent Inventor Helmut Dischler Neuss-Uedesheim, Germany Appl. No. 27,212 Filed Apr. 10, 1970 Patented Dec. 7, 1971 Assignee Becorlt Grubenausbau Gmbll Reckllnghausem, Germany Priority Apr. 12, 1969 Germany P 19 18 637.9

ELECTROMAGNETICALLY CLUTCHED PRESS 14 Claims, 10 Drawing Figs.

Int. Cl. 02k 7/11 Field 0! Search 310/80, 96,

98,99, 107, 110, 115,116, 83,94;3l8/l i4, 161; 100/289; 74/1255, 89.11, 89.1; 192/.02, 21.5

[56] References Cited UNITED STATES PATENTS 2,931,928 4/ 1960 Fehn, Sr. 310/95 3,356,874 12/1967 Chiapparelli 3l0/83 Primary Examiner-D. X. Sliney Attorney-Barman, Davidson and Herman ABSTRACT: A spindle press drive assembly using an electric motors rotor as an energy storing flywheel is characterized in that the electric power drives a second rotor acting as an energy storing flywheel and which is electromagnetically coupled to the first rotor so as to provide rotational energy therefor from the kinetic energy stored in the second rotor. The two rotors are disconnected at the end of the working stroke so that the second rotor remains rotating and only the energy of the first rotor is used during pressing. The two rotors may be coaxial or concentric and the second rotor may be independently rotated or rotated by electromagnetic forces between the two rotors. The disconnection can be achieved by a switch which senses the axial force occuring during deformation of a workpiece.

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PATENTEDIJEB. Hen 3.626222 SHEET, 7 OF 7 INVENTOR WELMUT b/S H ELECTROMAGNETICALLY CLUTCHED PRESS The invention relates to a drive for a spindle press, the rotatingly driven parts of which are connected to a rotor of an electric motor.

In some presses it is known to connect a spindle fitted with a flywheel to the rotor of an electric motor, which rotor can itself act as the flywheel. The spindle is mounted axially immovable in a housing. The shaft of the spindle has a steep thread on which a nut is threadedly engaged. The nut is axially displaceably but irrotationally mounted in a slide or other suitable guide device. The upper or moveable tool carrier of the press is connected with the axially displaceable nut.

During the working stroke of the press, the spindle and the flywheel connected thereto are rotated. This causes the nut and the upper tool carrier connected thereto to lower until the upper tool makes contact withthe workpiece. Thereupon, the axial movement of the nut is retarded, simultaneously slowing down the rotary movement of the spindle and the flywheel. The rotary energy stored in the flywheel is converted into axially exerted power which is available for use in deforming the workpiece. The return stroke of the press is effected either by reversing the direction of rotation of the driving rotor or by a spring or other suitable return means.

A press having a spindle directly driven by an electric motor, though having a number of advantages, has the disadvantages that the mains supply is loaded irregularly with short power surges, since the entire energy required for deforming the workpiece has to be supplied during the relatively short accelerating time of the spindle and the flywheel connected thereto. More particularly in high-speed impact presses the peak power demand during the downward movement of the spindle nut, is considerably greater than the mean power.

Therefore the object of the invention is to further develop an electric motor drive for a spindle press so that a substantially more even output is extracted from the mains supply. The object moreover, of the invention is to minimize energy peaks.

The present invention provides a spindle press drive assembly comprising anaxially movable irrotational part for connection to a movable tool carrier and a part rotatable by an electric motor, said motor having two rotors, one being connected to said rotatable part and the other being adapted to be rotated, the two rotors being adapted-to be electromagnetically coupled together to rotate the rotatable part to axially move said tool carrier to perform a working stroke but between working strokes being relatively rotated.

This other rotor can store energy during the intervals during the working strokes, i.e. during the return stroke of the upper tool carrier and the waiting period before the next working stroke, which energy can be tapped during the working stroke, which energy can be tapped during the working stroke, i.e. during the downward movement of the tool carrier. Since the time span between two working strokes is substantially greater than the duration of a working stroke, the supply is more evenly loaded.

The two rotors are conveniently coaxially arranged to simplify transmission of the extremely powerful moments from one rotor to the other. Furthermore, the two rotors can be located concentrically one in the other, the rotatably driven parts of the spindle press being connected with the inner rotor. This arrangement is advantageous because the outer rotor can receive in this manner a greater mass inertia moment without its weight having to be deliberately increased.

To allow sufficient energy to be stored in the outer rotor during the interval between two working strokes provision is made for the mass inertia moment of the outer rotor to be greater by a multiple, preferably tenfold, that of the mass inertia moment of the inner rotor.

In a preferred embodiment of the subject matter of the invention the electric motor used to drive the spindle press is a direct current motor with inner and outer rotors, the inner rotor of which is short-circuited during the working stroke of the spindle press; a direct current motor is particularly suitable for driving the spindle press because its output torque remains substantially constant at varying speeds. Owing to the short-circuit of the inner rotor during the working stroke of the spindle press the outer and inner rotors are inductively coupled together.

To drive the outer rotor between two working strokes of the spindle press, provision may be made either for the outer rotor to belong to a separate driving motor, or for the inner rotor to be connected to direct voltage during the interval between two working strokes of the spindle press. In the former case the outer rotor may be driven continuously whereby output peaks which can occur in a separate driving motor, may be compensated by the rotational energy stored in the outer rotor. With this method of driving the outer rotor it is, however, necessary to provide a separate device for the return stroke of the spindle press. In the second case the inner and outer rotors during the interval between two working strokes of the spindle press are oppositely accelerated by a driving moment acting between them. The direction of rotation of the inner rotor and the spindle connected thereto is consequently reversed to that during the working stroke. This causes the return stroke of the spindle press automatically until the spindle nut and the axially displaceable guide device connected thereto reach the upper stop. The spindle and the inner rotor connected thereto are herewith firmly and positively braked. The outer rotor is then further accelerated relative to the stationary inner rotor until it has again reached its nominal speed, to allow the next working stroke to be initiated.

The current to the direct current motor is conveniently supplied by collecting or slip rings.

The connection of the circuit of the inner rotor in accordance with a preferred embodiment of the subject matter of the invention is effected by means of switches rotating with the outer rotor. This prevents the powerful short-circuit current which is induced during the working stroke in the windings of the inner rotor having to be transmitted through the collecting rings. A thyristor for switching on and a power switch for switching off the short-circuit current are conveniently incorporated in the circuit for the inner rotor. The thyristor is made conductive to initiate the working stroke by supplying a firing or striking impulse. The power switch is closed until it is opened by the axial force acting on the spindle when the upper tool makes contact with the workpiece and thereby interrupts the short-circuit current. The inductive coupling between the outer and inner rotor during the working stroke is maintained in this-manner only during the period during which the spindle nut and the upper tool carrier connected therewith move downwards.

The thyristor is expediently rendered conductive also without contacts. In the embodiment of the drive using a separate driving motor for the outer rotor all the collecting rings may be dispensed with. Rendering the thyristor conductive without contacts may also be effected by means of a magnetic switch or a reed-relay switch. ln this case, however, it is necessary to incorporate a separate current source in the outer rotor which supplies the striking voltage for the thyristor. The magnet switch or reed relay switch in this case are actuated by the approaching of a magnet or a metal lug to the rotating outer rotor and close a separate firing or striking circuit for the thyristor. For supplying the firing or striking impulse to the thyristor without direct contact, the apparatus may alternatively incorporate an induction coil which is mounted on the outer rotor and in which on approach of a magnet to the rotating outer rotor generates the voltage necessary for causing the thyristor to conduct. By this means a voltage source rotating which the outer rotor is avoided.

ln accordance with a further embodiment provision is made for the electric motor to be a three-phase current motor with a short-circuited inner rotor, to the outer rotor of which during the working stroke of the spindle press a direct voltage is connected. By supplying direct current, the outer rotor and inner rotor are inductively coupled during the working stroke.

To drive the outer rotor of the three-phase current motor it is possible either to provide that the outer rotor of the threephase current motor is provided with a separate driving motor, or that the outer rotor of the three-phase current motor in the intervals between two working strokes of the spindle press is connected to a three-phase alternating current. In the first case the drive of the outer rotor can again be continuous, the output peaks in the additional driving motor may be compensated by the rotational energy stored in the outer rotor of the three-phase current motor. In this embodiment in turn separate measures for the return stroke of the spindle press have to be taken. In the second case the inner and outer rotor are driven in opposite directions of rotation after the working stroke, until the nut and the tool carrier connected thereto have reached their upper end position. Then the spindle and the inner rotor of the three-phase current motor are positively braked. Subsequently the outer rotor alone is accelerated relative to the fixed inner rotor until it has again reached its nominal speed and the next working stroke can be carried out.

The three-phase current motor in turn may conveniently be supplied with current by means of collecting rings.

Examples of the embodiments of the subject matter of the invention are described in detail below by way of the accompanying drawings.

IN THE' DRAWINGS FIG. 1 shows a spindle press driven by a direct current motor,

FIG. 2 is the electric circuit of the spindle press drive shown in FIG. 1,

FIG. 3 is a spindle press drive having a separate motor driving an outer rotor of a direct current motor,

FIG. 4 is the electric circuit of the spindle press drive shown in FIG. 3,

FIG. 5 and 6 show two arrangements for rendering a thyristor conductive without contacts,

FIG. 7 shows a spindle press drive having a three-phase current motor,

FIGS. 8 and 9 show an electric circuit for the press drive shown in FIG. 7, and

FIG. 10 shows an electric circuit of a spindle press drive with a three-phase current motor and a separate driving motor for an outer rotor of a three-phase current motor.

A description of specific embodiments will now be given. At the upper end of a housing or casing of a spindle press shown in FIG. 1, spindle 2 is mounted in bearing device 3, such as a thrust bearing, which allows the spindle 2 a slight axial play. Mounted on the spindle 2 is a spindle nut 4, the bore of which has a steep thread on the inside engaged with a corresponding thread on the outside of the spindle 2. An upper movable tool 6 is mounted on the lower end of an upper movable tool carrier 5. The tool carrier 5 together with the nut 4 is mounted axially displaceable in the housing I, but is prevented from rotary movement by a sliding spring 8 engaging in a groove 7 in the housing 1. A fixed lower tool 10 is carried by means 9 at the lower end of the housing and access (not shown) is provided to allow work pieces to be fed into the press.

The spindle 2 is connected above the bearing device 3 to an inner rotor 11 of a direct current electric motor 11, 12 whose casing is also rotatable and thus forms an outer rotor. The outer rotor 12 of this direct current motor like the inside rotor 11 is rotatably mounted. For the rotatable mounting of the outer rotor 12 there are used on the one hand a bearing device 13 which is arranged at the upper end of a supporting frame 14 mounted on the housing I, and on the other hand a bearing device 15 which engages around the connecting shaft between spindle 2 and inner rotor 11. The inner rotor 11 is rotatably mounted relative to the outer rotor 12 at the upper end in a bearing device 16, and at the lower end in the bearing device 15. The bearing devices 15 and [6 allow the inside rotor firmly connected to the spindle 2 a slight axial play which is equal to the play of the spindle 2 in the bearing device 3. The outer rotor 12 comprises a permanent magnet. Two collecting rings 17 and 18 are secured to the outer rotor 12 and serve to conduct current to the electric motor 11, 12. Moreover, a further collecting ring 19 is provided on the outer rotor 12 to supply current for a control circuit for short-circuiting the inner rotor. The current lead-in to the collecting ring 17, 18 and I9 is effected via collecting ring brushes or contacts 20, 21 and 22. A commutator 23 of the motor 11, 12 and collecting contacts 24 and 26 for supplying current to rotor 11 are located between the outer rotor 12 and the inner rotor 11, which are adapted to be rotatable in opposite directions to one another, on the upper end of the inner rotor 11.

Furthermore, in FIG. I a power switch 26 is shown which is firmly connected to the rotatable outer rotor 12, and an actuating member 27 of this switch engages against a collar 20 of the spindle 2 and is actuated by the axial movement of the spindle 2 made possible owing to the play of the bearing devices 3, l5 and 16. The function of the power switch 26, is explained further below. The electric circuit of the direct current motor 11, 12 shown in FIG. 1 shown schematically in F IG. 2. The electric leads between the collecting rings 17 and 18 and the commutator contacts 24 and 25 to the rotor 11 are shunted by a short-circuit circuit in which are incorporated the power switch 26 and a thyristor 28 rotating with the outer rotor 12. The firing or striking current for the thyristor 28 is supplied thereto through the collecting ring 19. In the circuit supplying the collecting rings 17 and 18, a two-point regulator 29 is incorporated, which may be used to regulate the speed of the inner rotor 11 relative to the outer rotor 12 by means of the voltage supplied thereto. In the current lead-in to the collecting ring 19, a strike or firing impulse generator 30 is incorporated, which is actuatable by a starter button 31. To supply current to the circuit shown in FIG. 2 a rectifier 32 is used which is connected to the main supply leads R.S.T.

The apparatus shown in FIGS. 1 and 2 functions as follows:

The spindle nut 4 is initially at its upper end position. A direct current is being supplied to the collecting rings 17 and 18, so that the outer rotor 12 is being accelerated relative to the stationary inner rotor until it has reached its nominal speed. This speed is kept constant by the two-point regulator 29. Then the starter button 31 of the firing impulse generator 30 is actuated. This causes a striking impulse to be supplied to the thyristor 28 via the collecting ring contact 22 and the collecting ring 19 hereby rendering it conductive. The power switch 26 is closed, so that the circuit of the inner rotor 11 is short-circuited. The rotating permanent-magnetically excited outer rotor 12 now induces a powerful induction current in the short-circuited winding of the inner rotor 11. The magnetic flux between inner rotor 11 and outer rotor 12 produced thereby causes the inner rotor 11 to be accelerated and carried along by the outer rotor 12 in the direction of rotation thereof.

The rotary movement of the inner rotor 11 and the spindle 2 connected therewith causes the spindle nut 4 and the upper tool carrier 5 connected thereto to be moved downwards until the upper tool 6 makes contact with the workpiece. When the upper tool 6 impacts the workpiece, a powerful upwardly acting force occurs in the spindle 2 causing the latter and the inner rotor 11 connected therewith to be upwardly displaced, to an extent allowed by the play of the bearing devices 3, 15 and 16. By this axial movement the actuating member 27 of the power switch 26 is urged upwards by the collar 2a, whereby the power switch 26 is opened, so as to break the short-circuited current. This simultaneously causes the disengagement of the inductive coupling between 11 and outer rotor 12 and the thyristor 28 to be extinguished.

The rotational energy stored in the spindle and the inner rotor 11 connected thereto and simultaneously acting as a flywheel in the subsequent complete braking and slowing down of the rotary movement is converted by the spindle 2 and the nut 4 into axially directed energy and is used during the deforming of the workpiece.

The outer rotor on the other hand owing to its inertia continues to rotate, and on account of its considerable moment of inertia relative to the inner rotor 11 during the acceleration of the inner rotor 11 loses only a small proportion of its rotary speed.

A direct voltage is nowagain connected to the collecting rings 17 and 18, so that the inner rotor 11 and the outer rotor 12 are accelerated relative to one another. The inner rotor 11 herewith rotates in the opposite direction of rotation to the outer rotor 12, so that the spindle nut 4 and the upper tool carrier 5 connected thereto are again upwardly displaced until the spindle nut 4 strikes against the upper end of the housing 1 and the spindle 2 and the inner rotor 11 connected thereto are firmly braked. The outer rotor 12 is now in its starting condition and is accelerated still more relative to the now firmly braked inner rotor 11, until it reaches its nominal speed again ready for the next working stroke of the spindle press.

To ensure satisfactory function of the power switch 26, it may be further expedient for the spindle 2 to be biassed by a powerful spring in the direction of action of the spindle press.

In the circuit controlled by the two-point regulator 29 a relay, not shown in the drawings, is also incorporated which switches off the direct voltage from the collecting rings 17 and 18 for as long as the armature circuit of the inner rotor 11 is short-circuited via the thyristor 28 and the power switch 26. This can be in the form of a no-volt relay sensing the back e.m.f. of the rotor 11.

The drive for the spindle press shown in FIGS. 3 and 4 corresponds substantially to the drive which has already been described by way of FIGS. 1 and 2. For parts corresponding to one another therefore the same reference numerals have been used, each increased by the amount of 100. In FIG. 3, an additional motor 150 is mounted on a supporting frame 114. This motor 150 is a three-phase motor and is used to drive a rotatable casing or outer rotor 112 of a direct current motor 111, 112. The three-phase motor 150 is constantly connected to the mains R.S.T. The temporary inductive coupling between the inner rotor 111 and the outer rotor 112 of the direct current motor is carried out by short-circuiting the circuit of the inner rotor through a thyristor 128 and a power switch 126. Since in the intervals between working strokes reacceleration of the outer rotor 112 is effected solely by additional threephase motor 150, it is necessary only to provide two collecting rings 117 and 119 on the outer rotor 112 to supply the striking voltage of the thyristor 128. Since the necessary output to cause the thyristor 128 to strike or fire is relatively small, a battery 133 may be used to energize a firing impulse generator 130.

The working stroke, i.e. the downwards movement of the spindle nut and the upper tool carrier connected therewith occurs as explained above in relation to FIGS. 1 and 2. The upward movement of the spindle nut and the upper tool carrier on the other hand, in the embodiment shown in FIGS. 3 and 4, has to be carried out after the working stroke by a return spring, which is not shown. This spring has to bias the spindle nut and the upper tool carrier respectively with an upwardly acting force.

FIGS. 5 and 6 show two electric circuits for making the thyristor conductive without contacts. These arrangements may be used both for the spindle press drive described in FIGS 1 and 2 and that of FIGS. 3 and 4. Particularly favorable is the use of making the thyristor conductive without contacts in the last mentioned case, since it enables collecting rings on the outer rotor 112 to be completely eliminated.

In the embodiment shown in FIG. 5 an induction coil 160 is incorporated in the firing circuit of the thyristor 128 and rotated with the outer rotor 112. A magnet 161 may be approached from the outside towards the rotating outer rotor 112. The striking voltage for the thyristor 128 is produced when the induction coil moves through the field of the magnet 161. After the thyristor 128 has ignited, the magnet 161 is withdrawn.

In the arrangement for making the thyristor 128 conductive without contacts shown in FIG. 6, a battery 170 and a reedrelay switch 171 are incorporated in the firing circuit of the thyristor 128, both of which rotate with the outer rotor 112. The rotating outer rotor 112 may be approached from the outside by a metal lug 172, whereby the switch 171 is closed and connects the firing voltage to the thyristor 128. Instead of switch 171 and the metal lug 172 a magnetic switch and a magnet may be used.

In the spindle press drive shown in FIG. 7 the driving motor is a three-phase motor with a short-circuited or squirrel cage inner rotor. Since the outer structure of the drive again substantially corresponds to that explained above by way of FIGS 1 and 2, here too for parts corresponding to one another the same reference numerals are used, which have been increased by the amount of 200. Both the inner rotor 211, which herein is a short-circuited or squirrel cage rotor, and an outer rotor 212 are mounted so as to be freely rotatable For supplying current to the outer rotor three collecting rings 217, 218, and 219 and collecting ring contacts 200, 221 and 222 are used.

FIG. 8 shown the electric circuit of the spindle press drive shown in FIG. 7. As shown in FIG. 8, a three-phase alternating current may be connected to the collecting rings 217, 218 and 219 through the switch 290. Moreover, a direct current from a mains (R.S.T) rectifier 232 may be connected to the collecting rings 218 and 219 through a switch 280. A power switch 226 is incorporated in the direct current circuit. The actuating circuit of the switches 280 and 290 is shown in FIG. 9. In this actuating circuit a starter switch (having normally open contacts 231a and normally closed contacts 231k) and a separate current relay 291 for the direct current circuit is provided. The electric circuit is shown in FIGS. 8 and 9 and operates as follows:

Initially the switch 290 is closed, so that the three-phase alternating voltage of the mains is connected to the collecting rings 217, 218 and 219 and that the outer rotor 212 has reached its nominal speed. The starter switch 321 is now actuated. This closes switch contacts 280 of the switch 280 and causes switch 290 to be released (see FIG. 9). A contact of the current relay 291 of the direct current circuit holds switch 280 in this position. The direct voltage now connected to the windings of the outer rotor 212 excites the latter and is inductively coupled to the inner rotor 211, so that the later is engaged by the rotating outer rotor 212 and the spindle nut is moved downwardly. The power switch 226 is closed during this downward movement. When the upper tool makes contact with the workpiece, as described above by way of FIGS. 1 and 2, the power switch 226 is opened, whereby the direct current circuit is broken. This causes the current relay 291 of the direct current circuit to open, so that the switch 280 is released and switch 290 is closed. Owing to the three-phase alternating current again being connected to the collecting rings 217,218 and 219, the inner rotor 21] and outer rotor 212 are again accelerated relative to one another, so that the spindle nut is again moved upwards and strikes against the upper stop, so that the spindle and the inner rotor 211 connected thereto are stopped. When the outer rotor 212 relative to the now stationary inner rotor 211 again reaches its nominal speed, the next working stroke may be carried out in the manner described. During each working stroke only as much energy is extracted from the rotating rotor 212 as is required to provide sufficient acceleration to the inner rotor.

FIG. 10 shown the electric circuit of a further embodiment of spindle press drive in accordance with the invention. For the parts already described by way of FIGS. 1 and 2 again the same reference numerals are used which have been increased by 300. As in the embodiment described in FIGS. 7 and 8 a three-phase motor with freely rotatable inner rotor 311 and outer rotor 312 is provided. The inner rotor 311 again being formed as a short-circuited or squirrel cage rotor. To drive the outer rotor 312 a separate three-phase motor 350 is used, which is connected permanently to a mains supply. For inductively coupling the inner rotor 311 to the outer rotor 312 during the working stroke in this example the windings of the outer rotor 312 are also connected to direct current from a mains (R.S.T.)fed rectifier 332. In the direct current circuit a switch 331 having associated therewith a hold-on current relay 331a and the power switch 326 rotating with the outer rotor 312 are incorporated. As in the example described above with a separate driving motor, herein too a return device is required by means of which the spindle nut after the working stroke is again upwardly displaced.

I claim:

1. A spindle press comprising a. means whereby a fixed tool can be carried b. displaceable tool carrier,

0. a casing,

d. a pair of threadedly engaged parts, one being connected to said displaceable tool carrier and being journaled in said casing for movement along an axis to approach the displaceable tool carrier to the fixed tool but being substantially irrotational and the other being substantially axially immovable but mounted for rotation about said axis in said casing,

a rotor connected to the rotational part another rotor windings on at least one of said rotors,

means for supplying energy said another rotor to cause it to rotate,

operable means for establishing a connection of the windings of one of said rotors whereby the two rotors are electromagnetically coupled together relatively nnrotationally with respect to each other so that said displaceable tool carrier executes a working stroke, and j. means operative to terminate said connection to disengage the coupling towards the end of each stroke.

2. A press according to claim 1, characterized by the feature that both rotors are coaxially arranged.

3. A press according to claim 2, in which the two rotors are concentric one within the other the rotational part being connected to the inner rotor.

4. A press according to claim 3 characterized by the feature that the moment of inertia of the outer rotor is a least 10 times the moment of inertia of the inner rotor.

5. A press according to claim 3 in which the connected rotor is the rotor of a direct current motor, and the operable means establishes for the working stroke a short circuit connection across the connected rotor.

6. A press according to claim 5, wherein the slip rings are provided to supply electric current to said connected rotor.

7. A press according to claim 6, wherein the said another rotor comprises a rotor of a separate electric motor and a part cooperating with said connected rotor for electromagnetic selective coupling therewith.

8. A press according to claim 7, wherein the short circuit connection is connected by switches rotating with the said another rotor.

9. A press according to claim 8, wherein a thyristor switch is used to make said short circuit connection and a mechanical switch is used as said operative means.

10. A press according to claim 9 wherein slip rings are provided on the said another rotor for firing the transistor switch.

11. A press according to claim 9 wherein means are incorporated on the said another rotor to fire the transistor switch in response to a magnetic field.

12 A press according to claim 1 wherein said connected rotor has a squirrel cage winding and wherein said another rotor has magnetic pole defining windings, said operable means being arranged to apply a direct current to said windings during the working stroke.

13. A press according to claim 12 wherein said magnetic pole defining windings are arranged as rotating field windings of an alternating current motor which windings are energized except during the working stroke.

14. A press according to claim 9 wherein said mechanical switch is arranged to sense a limited amount of axial play of said substantially axially im noy abl pa rt. 

1. A spindle press comprising a. means whereby a fixed tool can be carried b. displaceable tool carrier, c. a casing, d. a pair of threadedly engaged parts, one being connected to said displaceable tool carrier and being journaled in said casing for movement along an axis to approach the displaceable tool carrier to the fixed tool but being substantially irrotational and the other being substantially axially immovable but mounted for rotation about said axis in said casing, e. a rotor connected to the rotational part f. another rotor g. windings on at least one of said rotors, h. means for supplying energy said another rotor to cause it to rotate, i. operable Means for establishing a connection of the windings of one of said rotors whereby the two rotors are electromagnetically coupled together relatively nonrotationally with respect to each other so that said displaceable tool carrier executes a working stroke, and j. means operative to terminate said connection to disengage the coupling towards the end of each stroke.
 2. A press according to claim 1, characterized by the feature that both rotors are coaxially arranged.
 3. A press according to claim 2, in which the two rotors are concentric one within the other the rotational part being connected to the inner rotor.
 4. A press according to claim 3 characterized by the feature that the moment of inertia of the outer rotor is at least 10 times the moment of inertia of the inner rotor.
 5. A press according to claim 3 in which the connected rotor is the rotor of a direct current motor, and the operable means establishes for the working stroke a short circuit connection across the connected rotor.
 6. A press according to claim 5, wherein the slip rings are provided to supply electric current to said connected rotor.
 7. A press according to claim 6, wherein the said another rotor comprises a rotor of a separate electric motor and a part cooperating with said connected rotor for electromagnetic selective coupling therewith.
 8. A press according to claim 7, wherein the short circuit connection is connected by switches rotating with the said another rotor.
 9. A press according to claim 8, wherein a thyristor switch is used to make said short circuit connection and a mechanical switch is used as said operative means.
 10. A press according to claim 9 wherein slip rings are provided on the said another rotor for firing the transistor switch.
 11. A press according to claim 9 wherein means are incorporated on the said another rotor to fire the transistor switch in response to a magnetic field.
 12. A press according to claim 1 wherein said connected rotor has a squirrel cage winding and wherein said another rotor has magnetic pole defining windings, said operable means being arranged to apply a direct current to said windings during the working stroke.
 13. A press according to claim 12 wherein said magnetic pole defining windings are arranged as rotating field windings of an alternating current motor which windings are energized except during the working stroke.
 14. A press according to claim 9 wherein said mechanical switch is arranged to sense a limited amount of axial play of said substantially axially immovable part. 